Slotted metal pipes, or tubulars as they are often known, have been used for a considerable length of time in oil, gas and water wells as a means to limit the amount of sand or debris allowed to enter the tubular as oil, gas or water is drawn in from surrounding underground formations. The slotted tubulars effectively act as a liner and screening mechanism to permit the desired fluid to be drawn into the tubular for extraction while excluding sand, rock and other particles. Tubular liners must have slots that are sufficiently small in width to prevent particulate matter from entering the pipe, while maintaining sufficient structural integrity to withstand pressures to which they may be subjected in underground environments, particularly in wells having horizontal components.
The difficulty encountered with slotted tubulars is not so much in their use but in their method of manufacturing. The particular underground formation within which the tubular is to be deployed will for the most part dictate a maximum slot width that will be acceptable. In oil and gas well applications, it is often the case that the oil or gas being targeted is located in formations comprised of fine sand particles. In such situations it is not unusual to require a slot width in the tubular of 0.010 of an inch, or less. Unfortunately, conventional manufacturing equipment is rarely capable of cutting slots in tubulars having a width less than 0.015 inches. As a result, manufacturers commonly subject slotted tubulars to a secondary seaming process where rollers are used to apply pressure to the tubular in the vicinity of the slot, having the result of narrowing the slot width at the exterior surface and forming a slot with a keystone, parabolic, or similar shaped profile.
A variety of different seaming methods have been proposed by others as a means to reduce the width of slots formed in tubulars through conventional mechanical methods. Such methods include those described under U.S. Pat. No. 6,112,570, dated Sep. 5, 2000; Canadian patent 2,183,032, dated Jul. 17, 2001; and, Canadian patent 2,324,730, dated Aug. 12, 2003.
Although the seaming methods that have been used by others have been generally successful, they also suffer from a number of inherent limitations. First, the equipment necessary to perform the seaming operation is relatively complex and often necessitates a precise alignment of seaming rollers on the surface of the tubular in order to ensure a full and complete seaming of all slots. To successfully narrow each slot, the feed rate of the tubular through the seaming equipment must also be kept relatively low, resulting in a low production rate. In an attempt to avoid the necessity of precise alignment of the seaming rollers with the slots in the tubular, some have suggested moving the seaming rollers in a helical sweeping pattern across the entire surface of the tubular. While doing so may alleviate the need for precise alignment of the rollers, it also results in the entire surface of the pipe being contacted by the seaming rollers, a process that once again is time consuming and results in a relatively low throughput. The equipment utilized is also expensive and adds significantly to the capital commitment on the part of the manufacturer.